Ocean-covered planets may not be the places to search for life

By Shannon Hall

Although water worlds are awash with one of the key ingredients for life, surprisingly, they might not be the best places to find it.

Tessa Fisher, a graduate student at Arizona State University in Tempe, and her colleagues presented this counter-intuitive idea last week at the Habitable Worlds conference in Laramie, Wyoming. Her research shows that a planet soaked in oceans could be starved of phosphorus – a major component of DNA and other important molecules.

Unlike other essential nutrients for life, phosphorous is hard to find. It’s mostly locked away in rocks, so it only becomes accessible when rainfall splatters those rocks and flushes phosphorous into water where it can be used by microbes.

Although rainwater is quite efficient at dissolving phosphorus, seawater is not. And that’s a problem for worlds entirely covered by salty seas. Without any exposed land, there will be far less phosphorous available for fledgling life. Fisher and her colleagues have estimated that these worlds will have three to four times less phosphorous in their oceans than seas on Earth.

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